(iii) In order to ensure a sufficient efficiency of wash-in leptogenesis, one only needs to assume that the standard RHN decay parameters \(K_{i\alpha }= \Gamma _{i\alpha }\left(T=0\right)/H\left(T=M_i\right)\) , which normally quantify the efficiency of wash-out processes, are large enough.
In other words, wash-in leptogenesis is particularly efficient in regions of parameter space that are otherwise characterized by a large asymmetry wash-out.
We refer to this parameter regime, otherwise known as the strong wash-out regime, as the strong wash-in regime.
In the type-I seesaw model, light-neutrino masses of \(\mathcal {O}\left(0.1\right)\,\textrm {eV}\)  imply RHN decay parameters as large as \(K_{i\alpha } \sim 10\cdots 100\)  and hence naturally point to this regime (see, e.g., Ref. [1]}).
As shown in Ref. [2]}, the result in Eq. (REF ) is in this case in excellent agreement with the exact solution that one may obtain by explicitly solving the Boltzmann equations for the three flavored \(B\!-\!L\)  charges at the time of RHN decay.
In the strong wash-in regime, any deviations from Eq. (REF ) are exponentially suppressed by factors of the form \(e^{-c_{i\alpha }K_{i\alpha }}\)  with some coefficients \(c_{i\alpha }\) .
This situation changes in the weak wash-in regime, i.e., if we choose weaker RHN couplings, such that only a fraction of the totally available asymmetry is washed into the plasma, requiring one to resort to a description in terms of Boltzmann equations [2]}.
In the following, we will, however, ignore this possibility and focus on the strong wash-in regime, which is well motivated by the low-energy neutrino data.
